Stop-motton detector for detecting the condition of bobbin thread in a sewing machine



Jan. 19, 1960 E. vossEN 2,921,546

STOP-MOTION DETECTOR FOR DETECTING THE CONDITION OF BOBBIN THREAD IN A SEWING MACHINE Filed April 16, 1956 5i H: LE

a m n llllllllllllllll' H0 64 50 a 74 I a 32 34- I I L |l 38 6O INVENTOR ATTORNEY EDWARD VOSSEN.

United rates Patent Edward Vossen, Malverne, N.Y., assignor to Stop-Motion Devices C0rp., Brooklyn, N.Y., a corporation of New York Application April 16, 1956, Serial No. 578,330

1 Claim. (Cl. 112-219) This invention relates to a stop-motion detector for detecting the condition of bobbin thread in a sewing machine. It constitutes an improvement over the thread detector which is shown and described in my co-pending patent application Serial No. 358,822, filed June 1, 1953, now Patent No. 2,747,039.

In the present case as in said patent application, the purpose of the thread detector is to detect and signal a break in the bobbin thread or any unusual slack condition of said thread, as when the bobbin is nearly spent. The thread detector in said patent application is shown to be mounted on the head of a sewing machine and therein lies a difficulty. The detector is provided with a sensitive probe or feeler which must be very precisely positioned with respect to the presser foot, needle and thread. Different conditions are encountered when the fabric being sewn is thick and heavy or light and thin and when it is sewn in a single layer or in multiple layers, as when two pieces of fabric are sewn together or binding is applied to the edges of the fabric. The raising or lowering of the presser foot normal to all sewing operations also poses a problem with respect to the positioning of the thread detector.

In the case of the thread detector disclosed in said patent application, therefore, it is not only ditficult to initially position said thread detector on the head of the sewing machine, but it is also necessary to continually adjust or shift its position to adapt it to the varying and different conditions above mentioned.

It is the principal object of the present invention to provide a bobbin thread detector which is mounted (by clamping, screwing or other means) on the presser foot or presser bar (rod) as distinguished from the stationary head of the sewing machine. For the purposes of the specification and claims, it will be understood that whether the threaddetector is secured directly to the presser foot or directly to the presser bar (rod) it is in eifect secured to both.

The difficulty above described of accurately positioning the thread detector is thereby entirely eliminated since the relationship between said detector and the presser foot remains constant irrespective of the nature of the fabric and the number of its layers which may constitute the work. When the presser foot is elevated, the detector moves with it and when the presser foot is lowered again the detector moves with it so that at all times and under all conditions the spatial and positional relationship between said detector and said pressure foot remains and the rough motion of the presser foot which is nor mat to all sewing machines in operation, have heretofore mutually excluded each other so as to prevent the mounting of such detector upon the presser foot.

It is accordingly an important object of this invention to provide a thread detector of the character described, whose probe or feeler is sufiiciently sensitive for detection purposes, but which is nonetheless unaifected by the vibratory and reciprocating movements of the presser foot. Stated differently, the present invention provides a detector whose probe or feeler is sensitive to a slack or other abnormal condition of the bobbin thread but which is not sensitive to these extremely rough movements of the presser foot.

The key to a mechanism which is so sensitive in one respect and so unresponsive in another may be found in the employment of two spring-urged bell cranks working against each other, The first bell crank is the probe itself which is shaped to bell crank form and which is pivoted in hell crank fashion. The other bell crank is the switch arm which closes the stop motion circuit when the probe encounters an abnormal thread condition. In addition to this function, said second bell crank normally engages the first bell crank and holds it in operative position, ready to-detect any such abnormal thread condition. When said first bell crank (the probe) is tripped by reason of an abnormal thread condition, it, in turn, trips the second bell crank (the switch arm) which then engages a contact member to close the switch.

Still another object of this invention is the provision of a thread detector of the character described whose probe arm normally occupies a horizontal position and pivots on a horizontal axis transverse to the path of feed of the machine, so that when said probe arm is actuated upon encountering an abnormal thread condition, its arcuate movement will not bring it any closer to the sewing machine needle than it is in its stationary operative position. This feature should be contrasted with the arrangement of parts shown in my said co-pending patent application wherein the probe arm normally occupies an inclined position with its pivotalaxis situated above the probe portion proper; When such probe is actuated, it swings upwardly and is thereby brought closer to the needle than it originally was in its stationary operative position. Consequently, to avoid conflict between the probe and the needle, it is necessary to positionrit a greater distance from the needle than the arrangement in the present application requires. In this connection it will be understood that the closer the probe is tothe needle, the more efficient and effective is it as a detector of abnormal thread conditions.

The invention is illustrated in the accompanying drawing in which:

Fig. 1 is a side view of a thread detector made in accordance with this invention, showing it mounted upon the presser foot of a sewing machine.

Fig. 2 is a top view thereof.

Fig. 3 is another side view of said thread detector.

'Fig. 4 is a vertical section on the line 4-4 of Fig. 3.

Fig. 5 is a sectional view on the line 5-5 of Fig. 3, being also a top view of said thread detector with its upper supporting plate or bracket removed therefrom.

Fig. 6 is a vertical section on the line 66 of Fig. 5.

The sewing machine head 10 shown in Fig. 1is intended to illustrate all conventional heads of all conventional sewing machines and to indicate that the stopmotion thread detector 12 is applicable to all such heads of all such machines. It will be observed that said detector is attached to the presser bar 14 which supports the presser foot 16 by the same screw 18 which secures said presser foot to said presser bar. Consequently,

said detector is attached by said screw both to the presser bar and the presser foot.

In the illustrated form of the invention, the thread detector 12" is provided with a supporting plate or bracket20 of generally .!.'.-shape and it will be noted that said. plate or bracket consists of a horizontal flat plate portion 22 and a vertical portion 24 which is arcuate in shape to conform to the curvature of the presser bar 14., This is shown in Fig. 2. Fig. 4 shows that an elongated vertically extending slot 26 is formed in the vertical component 24 of the L'shaped bracket iii. It is through said slot that the shank of the screw 18 projects and it will be understood that said elongated slot renders it possible'to adjust the vertical position of said L-shaped bracket, and hence of the entireldetector assembly, relative to the presser foot and the presser bar.

Detector 12 is provided with a' casing 36 having a pair of side walls 32 and 3.4 respectively; The horigpntal component 22 of the supporting plate or bracket O'serves as thetop wall of said casing and there is also cttom wall 36. It will be observed in Fig. 6 that said botto wall 36 constitutes a flat platewhose forwardly extending end 38 is curved upwardly to facilitate the flow of the work below it. There is also a front wall 40 and a rear wall 42. The entire casing, save for said rear wall 42, may be made, preferably, of machined, stamped or cast metal, although molded plastics would tudinal axis of shaft 52.

This is the first bell crank of the mechanism herein described and claimed.

The second bell crank 70 is best shown in Figs. 5 and 6. It consists of a plate of inverted L-shape, having an upper horizontal component??? and a downwardly extending vertical component 74-. This second bell crank is secured toza shaft 76 which is also journaled into the side walls of the casing. wardly extending end of the horizontal component 72 is bent over l. ally to form an arm '78 which is engageaole with tr verse portion 66. of probe wire 56. This may be observed in Figs. 4, 5 and -6. A tension spring 80 is secured at its upper end to horizontal component also besatisfactory. Rear wall 42, however, should preferably be made of dielectricmaterial, such as fiber block or a'suitable plastic material, since it supports some of the electrical components of the switch.

. Reference to Fig. 2 will show that the horizontal plate 22 of bracket 2i) is provided with a-pair of parallel, longitudinally extending slots 44 and 46 through which screws 48 and 50 project. These screws secure the casing, and more particularly its side walls 32 and 34, to said bracket 20 and the elongated shape of said slots renders it possible to adjust"the position of said casing horizontally with respect to said bracket 26 and hence with respect to the presser bar and presser foo-t. This adjustment, together'with the vertical adjustment above mentioned, renders it possible to adjust the horizontaland 72 of bell crank 70 and it is secured at its lower end to a rod 82 which is secured to the side walls of the casing.

it will now be understood that the action of spring 89 is to urge the second bell crank 7% to move in counterclockwise direction as viewed in Fig. 6. When the two bell cranks are in their Fig. 6 positions, the second bell crank 7d, and more particularly its transverse end portion i fi'en gages the transverse portion 66 of the first bell crank 56 and prevents said' first bell crank from swinging in clockwise direction as viewed insaid F1g. 6.

The first bell crank or probe 56 is now supported in operative position adjacent the needle Qlland thread d2 of the sewing rnachine representedby head 1d. Said grroise, and more particularly its transverse end portion lift and its longitudinal component 62, occupy generally horizontal positions parallel to. the base 94 of the machine. When the bobbin thread breaks or becomes unduly slack for one. reason oranother, as when thebobbin is nearly spent, th read'?2 assumes acant'ed position represented by the interrupted lines 96 .in Fig. 1. lit now engages the probe portion ,Giilcf probe, 56 and carns it upwardly. This has the effect of turning the. entire. probe 56 in clockwise direction as viewed in Fig. 6 and thereby disengages its transverse portion 66. from the transverse end portion 73 of the second bell crank 7t vertical positions of the thread detector and to a'ccurately position it relative to, the thread, needle and presser foot. It will be understood that an additional side plate or cover may be attached to the left side of the casing as viewed in Fig. 2 in order to enclose the outwardly extending moving parts and to sealoif the openings in said side of the casing against dust and lint and other foreign matter. A shaft 52 is journaled into the side walls 32 and 34 of the casing so as to be adapted to engage in angular movement about its longitudinal axis. A coiled torsion spring 54 is mounted on said shaft and connected to i the casing in order to urgesaid shaft 52 to turn in clockwise direction as viewed in Figs. 1 and 3.: A wire 56 is looped around said shaft as: is clearly shown in Figs.

'3' and 4 and the-looped portion 58 is spot welded or of th,e other portions of wire56 extend generally hori- Q l aHy. vIt will now be observed from the view of Ei -l. 3i'th atiwire 56, which will hereinafter be known hal -.1 61 Probe or feeler of the present device, constitutes a, hel cranks whose pivotal axis coincides with the longitwo blades or leavesyi iti are inclined towardeach other The second bell crank/Wis now free to swing in counterclockwise direction as viewedin Fig. 6 and this it does underthe influence of spring 84}. It will now be understood that the vertical component 7 of said. second bell crank 7i? serves as a switch arm or blade relative to switch contact members this; These contactv members Hill) are simply a pairof leaves with some inherent spring qualities, 7 which are supportedi on fiber block by means of screv/"1il2 or by other suitable means. The

' as viewedin Fig.5 and theylare'spacedslig tly from each other in order toaccorn'modate the blade 'Z i'when said second bell crank '70 swings in' counter-clockwise I directionf a s aforesaid. A conductor. may be connected by m earrs of screw 162" to the contactfmembers 1'90 and a mechanism when contact is contactmembers 1%.

in conventional manner this would leadfto the stop motion mechanism to close the circuitj'and actuate said made between blade 74- and 'Tofacilitate entryof blade 74 into the space between contact members 1%, the operative edge of said blade is beveled to a tapered or wedge-shaped portion llild. This is best seen in Fig.5. The result is thatvery little force is required to urge said blade 74 between said contact rnernbers 1% and a relatively weak spring St will do the trick; 7 This is important because a strong spring would cause the transverse portion 78 of the second bell crank 70 to exert undue pressure upon the transverse portion 66 of the first bell crank or probe 56, thereby interfering withits inovernent in clockwise direction as viewed in Fig. 6 under the influence of thread 92. The nature of theengagement between blade74 and contact members 1% is also important in the following respect: It is a wiping-type of engagement which not only provides' the necessary electrical contact but also keeps the contact members andthe blade it clean of lint or any other'foreign' matter that may enter the casing It will be seen that the for- To reset the device after it is actuated as above described by the thread 92, all that need be done is to return said thread to its normal vertical position out of engagement with probe 56 and to return the second bell crank 70 to its Fig. 6 position. This is done by means of a knob 110 which is secured to shaft 76. It will be understood, that once probe 56 is freed from thread 92, it will return to its original position as shown in Fig. 6 under the influence of torsion spring 54. When knob 110 is turned to return the second bell crank 70 to its Fig. 6 position, transverse portion 78 cams past transverse portion 66 and resumes its Fig. 6 position, thereby holding the second bell crank 70 and more particularly its blade portion 74, out of engagement with the contact members 100.

The foregoing is illustrative of a preferred form of this invention and it will be understood that this preferred form may be modified and other forms may be provided within the broad spirit of the invention and the broad scope of the claim.

I claim:

A thread detector for a sewing machine having a presser bar and a presser foot connected to said presser bar, said thread detector being adapted to be removably mounted on said presser bar and comprising a casing, a

thread feeler, a movable electrical contact member, and

a fixed electrical contact member, said feeler comprising a bell crank which is pivotally supported on said casing, one arm of said bell crank projecting horizontally forwardly into operative position adjacent the presser foot, the other arm of said bell crank projecting vertically upwardly in said casing, said movable electrical contact member comprising a second bell crank, said second bell crank being pivotally mounted in said casing, one arm of said second bell crank being engageable with the vertically extending arm of the first bell crank, the second arm of the second bell crank being engageable with said '6 1 fixed contact member, said second bell crank being springurged for movement in the direction of the fixed contact member to bring its second arm into engagement therewith, said first bell crank being normally positioned to block such movement save when it is tripped by the sewing machine thread at which time it is dislodged from such blocking position to free the second bell crank for such movement, said thread detector being adapted to be adjustably secured to the presser bar by means of an L- shaped bracket, said bracket having a vertical component with a vertically extending slot formed therein and a horizontal component with a horizontally extending slot formed therein, said bracket being adapted to be secured to said presser bar for vertical adjustment relative thereto by means of a screw engaging said presser bar through said vertically extending slot of the vertical component of said bracket, said thread detector being adjustably secured to the horizontal component of said bracket by means of a screw projecting through said horizontally extending slot for horizontal adjustment of said thread detector toward and away from said presser foot, said presser bar having a curved surface in the area of its engagement with the vertical component of the bracket, said vertical component being provided with a complementary curved surface adapted to fit the curvature of said presser bar to prevent accidental angular dislodgment of said bracket relative to said presser bar about the axis of the screw which secures said vertical com ponent of the bracket to said presser bar.

References Cited in the file of this patent UNITED STATES PATENTS 747,165 Greist Dec. 15, 1903 1,455,387 Cobb May 15, 1923 2,387,958 Vossen Oct. 30, 1945 2,643,305 Mansson June 23, 1953 2,796,035 Bryson June 18, 1957 

